When power is amplified by using an amplifier such as a high power amplifier (hereinafter referred to as “HPA”) or the like, desired input-output characteristics may not be obtained due to nonlinear distortion characteristics of the amplifier.
In particular, when the frequency of a radio signal to be amplified is high, in order to linearize the amplifier by compensating for the nonlinear distortion characteristics, the amplifier needs to be subjected to predistortion for canceling the nonlinear distortion characteristics of the amplifier by using digital signal processing. Such predistortion requires a monitor signal obtained by monitoring an output of the amplifier.